Non-run­ning is­sue

Car Mechanics (UK) - - Diagnostics Doctor -

I hope you can help me with my 2002 BMW E39 5-Se­ries 2.2 petrol with the M54 en­gine and man­ual trans­mis­sion. It has done 98,000 miles. The car cranks strongly, but doesn’t start – the en­gine doesn’t fire at all. The car was driv­ing per­fectly the night be­fore it re­fused to start and there were no signs of any­thing wrong – en­gine noises, over­heat­ing, etc – and it has al­ways started first time be­fore. When I crank, the rev counter doesn’t move. The en­gine man­age­ment light is not il­lu­mi­nated and there are no other warn­ing lights show­ing on the dash. I’ve put a di­ag­nos­tic tester on it, but there are no codes logged.

I have checked the bat­tery and it’s show­ing 11.8 volts. I’ve put a known good bat­tery on it from an­other car and it still cranks, but won’t start. I fully charged the BMW bat­tery to 12.8V, but it made no dif­fer­ence. I checked the cold crank­ing with a mul­ti­me­ter and it dropped to 10.72V – does that seem OK?

I don’t think it’s an im­mo­biliser prob­lem, as the car recog­nises the key when I turn it over. I’ve checked the fuel pres­sure at the Schrader valve and fuel came out at quite a good pres­sure. I sprayed some Easy Start into the in­take, to no avail.

I can’t hear the fuel pump prim­ing, but can’t be sure. There are two fuses listed for the fuel pump – I’ve checked both and they’re OK. I’ve un­plugged the MAF sen­sor, but that made no dif­fer­ence. I’ve checked for spark on one of the cylin­ders and there was a good spark show­ing. I’m think­ing it could be the crank­shaft po­si­tion sen­sor, but I don’t want to re­place this sen­sor need­lessly as they are quite ex­pen­sive. Can the sen­sor be checked us­ing a mul­ti­me­ter? What sort of re­sis­tance should a healthy sen­sor show?

I’m also hope it’s not the tim­ing chain, but I un­der­stand th­ese usu­ally rat­tle long be­fore they let go. Ian Rim­mer From the data I have on your BMW, the im­mo­biliser pre­vents the starter from op­er­at­ing, so be­cause your ve­hi­cle cranks over, this can be dis­counted.

The fuel sys­tem should run at a pres­sure of 3 Bar and this should be checked us­ing a proper pres­sure gauge fit­ted to the Schrader valve. A lower pres­sure will still pro­duce a spray when the valve is de­pressed, but it may not be enough to start and run the en­gine. As you can­not hear the fuel pump op­er­at­ing, I would first check the fuel pump re­lay, which ac­cord­ing to Au­to­data should be re­lay num­ber 2 lo­cated in the load area.

If the re­lay is not at fault then I would sus­pect the crank­shaft sen­sor or pos­si­bly the camshaft sen­sors, but I am slightly con­fused by the lack of codes. I would ex­pect a pend­ing code to be held some­where in the sys­tem. Al­though you do not men­tion which code reader you are us­ing, it may be that you will need an of­fi­cial BMW reader to find the pend­ing codes.

Be­fore test­ing the sen­sor, you should check the re­sis­tance of the loom be­tween the sen­sor and the ECU – this should be be­low 1 ohm. The sen­sor pins on the ECU should be num­bers C21 and C8. This is the cen­tral bank of pins on the ECU and the pins are num­bered from left to right start­ing at the low­est row of pins on the ECU.

Test­ing the ac­tual sen­sor would re­quire an os­cil­lo­scope to check the wave­form be­ing pro­duced. This should be a steady and even square wave formed as the sen­sor passes the pick-up.

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